Fractographic discussion on fracture toughness test specimen in transition temperature region

Steels which are used in an intense neutron irradiation have a tendency to increase their ductile-brittle transition temperature as a result of material degradation. The Jic test, which is used to evaluate the plane strain fracture toughness using small size specimens, cannot be applied at the temperature. In order to clearly identify the fracture mechanism and to prove the formerly proposed, modified Jic test procedure ( Ohtsuka 1984 ) in the temperature region, the fracture toughness test and the partial loading and unloading test were both conducted. Fracture surfaces of these test specimens were observed stereographically and the elastic stress distribution around the crack tip was then discussed.